Novel computation enables best-yet estimate of ground state of neutral helium. (News Briefs).A NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. scientist, in collaboration with Indiana University Indiana University, main campus at Bloomington; state supported; coeducational; chartered 1820 as a seminary, opened 1824. It became a college in 1828 and a university in 1838. The medical center (run jointly with Purdue Univ. , has computed the nonrelativistic energy for the ground [S.sup.1] state of neutral helium to be -2.9037 2437 7034 1195 9829 99 a.u. This represents the highest accuracy computation of this quantity to date. Comparisons with other calculations and an energy extrapolation (mathematics, algorithm) extrapolation - A mathematical procedure which estimates values of a function for certain desired inputs given values for known inputs. If the desired input is outside the range of the known values this is called extrapolation, if it is inside then yield an estimated uncertainty of [10.sup.-20]. Exact analytical solutions to the Schrodinger equation Noun 1. Schrodinger equation - the fundamental equation of wave mechanics Schrodinger wave equation differential equation - an equation containing differentials of a function , which determines such quantities, are known only for atomic hydrogen and other equivalent two-body systems. Thus, solutions must be determined numerically. How this best calculation to date was accomplished is in an article submitted to the International Journal of Quantum Chemistry The International Journal of Quantum Chemistry is an international peer-reviewed scientific journal publishing original, primary research and review articles on all aspects of quantum chemistry, defined as "Theory and Computation in Chemistry, Physics, and Molecular Biology". . To obtain this result, very large basis sets must be used. In this case, variational expansions of the wave function with 4648 terms were employed, leading to the need for very large computations. Such large expansions also lead to problems of linear dependence, which can only be remedied by using higher precision arithmetic than is provided by standard computer hardware. For this computation, 192 bit precision (roughly 48 decimal places) was necessary, and special coding was required to simulate hardware with this precision. Parallel processing parallel processing, the concurrent or simultaneous execution of two or more parts of a single computer program, at speeds far exceeding those of a conventional computer. was also employed to speed the computation, as well as to provide access to enough memory to accommodate larger expansions. NIST's Scientific Computer Facility cluster of 16 PCs running Windows NT was utilized for parallel computation. Typical run times for a calculation of this size about are 8 hours on a single CPU CPU in full central processing unit Principal component of a digital computer, composed of a control unit, an instruction-decoding unit, and an arithmetic-logic unit. , but only 30 min to 40 min on the parallel processing cluster. This work employs a very novel wave function, namely, one consisting of at most a single [r.sup.12] raised to the first power combined with a conventional nonorthogonal configuration interaction basis. The researchers believe that this technique can be extended to multielectron systems. Work is in progress, for example, to see what uncertainties can be obtained for atomic lithium, which is estimated to require a 6000-fold increase in CPU requirements to reach the same level of precision, making the use of parallel programming techniques even more critical. CONTACT: James Sims, (301) 975-2710; james.sims@nist.gov. |
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